This invention relates generally to a system for selectively interposing color separation filters in an electrophotographic print mechanism or engine for the making of color copies, and relates particularly to a system in which the individual color filter assemblies are drawn into an optical path by a belt running beneath a track which extends from the optical path to the home position of the filter assemblies.
The electrophotographic print engine is a machine that is used for making xerographic, i.e. dry copies. The process used to make xerographic copies and color xerographic copies is well known in the art. The print engine makes the copy by focusing an optical image of an original to be copied onto an electrically charged photosensitive medium known as a photoreceptor. This process creates an electrostatic charge on the photoreceptor in the image of the original. This image is passed near to a source of toner materials which are attracted to the electrostatic image and migrate to the image. The image is then transferred to an image receptor, which is usually a sheet of paper. The image receptor is then passed through a fusing device that melts the toner, which is usually a plastic that melts at a predetermined temperature, onto the image receptor, thus creating the xerographic copy.
In order to create a color copy of the original, a set of color separation filters are individually interposed in the optical path between the optical image and the photosensitive medium. A different color toner, which corresponds to each filter, is used. The electrostatic image is passed near to the toner which corresponds to the color filter which was first interposed in the optical path. The developed image is then transferred to the image receptor. However, in full color electrophotography, instead of immediately passing the image receptor through the fuser, the process of transferring the image of the original to the image receptor is repeated for each filter. Normally, there are three different colored filters and three different color toners. Only then is the image receptor passed through the fuser and the color copy results. Therefore, it can be seen that the mechanism for selectively interposing the color filters in the optical path is of prime importance in an electrophotographic print engine designed for making color xerographic copies.
The typical system for selectively interposing color filters in an electrophotographic print engine involves placing the color filters in a large disc and then rotating the disc around a central axis, through the use of a motor of a type well known in the art, so that the filters are sequentially positioned in an optical path. The optical image of the item to be printed can then be focused through the filter onto a photoreceptor. This process is repeated for each color filter until a full color image is placed on the photoreceptor. The image is then transferred onto a medium for receiving the copy such as paper or transparent plastic.
Another system used for selectively interposing color filters is a mechanism in which the color filters are attached about a single rod. The filters radiate out from the rod in a spaced apart manner. To selectively interpose the color filters, the rod is rotated, again through the use of a motor of a type well known in the prior art, so as to sequentially position the color filters in the optical path. The color image is then placed on the photoreceptor in the manner well known in the art.
Both of these systems suffer from distinct disadvantages. Both systems require a great deal of room to operate, creating limitations on possible size reduction of the print engine and causing the print engine to occupy a significant amount of space in the use area. This in turn results in an increase in the weight of the print engine. Another problem with these systems is that the increase in size and weight increases the power consumption necessary to operate the print engine. These systems also require precise machining of the component parts to position the filter in the correct place in the optical path, increasing the likelihood of malfunction of the system. All these disadvantages have the necessary result of an increase in the cost of the print engine.
Thus, there is a need for a smaller, less cumbersome system for interposing color filters in an electrophotographic print engine which requires a minimal amount of power to operate and a minimal amount of precise machining in the manufacture of the system.